Tcl includes a library of Tcl procedures for commonly-needed functions.
The procedures defined in the Tcl library are generic ones suitable
for use by many different applications.
The location of the Tcl library is returned by the info library
command.
In addition to the Tcl library, each application will normally have
its own library of support procedures as well; the location of this
library is normally given by the value of the $app_library
global variable, where app is the name of the application.
For example, the location of the Tk library is kept in the variable
$tk_library.

To access the procedures in the Tcl library, an application should
source the file init.tcl in the library, for example with
the Tcl command

source [file join [info library] init.tcl]

If the library procedure Tcl_Init is invoked from an applications
Tcl_AppInit procedure, this happens automatically.
The code in init.tcl will define the unknown procedure
and arrange for the other procedures to be loaded on-demand using
the auto-load mechanism defined below.

Determines whether there is an executable file or shell builtin
by the name cmd. If so, it returns a list of arguments to be
passed to exec to execute the executable file or shell builtin
named by cmd. If not, it returns an empty string. This command
examines the directories in the current search path (given by the PATH
environment variable) in its search for an executable file named
cmd. On Windows platforms, the search is expanded with the same
directories and file extensions as used by exec. Auto_exec
remembers information about previous searches in an array named
auto_execs; this avoids the path search in future calls for the
same cmd. The command auto_reset may be used to force
auto_execok to forget its cached information.

auto_import pattern

Auto_import is invoked during namespace import to see if
the imported commands specified by pattern reside in an
autoloaded library. If so, the commands are loaded so that they will
be available to the interpreter for creating the import links. If the
commands do not reside in an autoloaded library, auto_import
does nothing. The pattern matching is performed according to the
matching rules of namespace import.

auto_load cmd

This command attempts to load the definition for a Tcl command named
cmd. To do this, it searches an auto-load path, which is
a list of one or more directories. The auto-load path is given by the
global variable $auto_path if it exists. If there is no
$auto_path variable, then the TCLLIBPATH environment variable is
used, if it exists. Otherwise the auto-load path consists of just the
Tcl library directory. Within each directory in the auto-load path
there must be a file tclIndex that describes one or more
commands defined in that directory and a script to evaluate to load
each of the commands. The tclIndex file should be generated
with the auto_mkindex command. If cmd is found in an
index file, then the appropriate script is evaluated to create the
command. The auto_load command returns 1 if cmd was
successfully created. The command returns 0 if there was no index
entry for cmd or if the script did not actually define cmd
(e.g. because index information is out of date). If an error occurs
while processing the script, then that error is returned.
Auto_load only reads the index information once and saves it in
the array auto_index; future calls to auto_load check for
cmd in the array rather than re-reading the index files. The
cached index information may be deleted with the command
auto_reset. This will force the next auto_load command to
reload the index database from disk.

auto_mkindex dir pattern pattern ...

Generates an index suitable for use by auto_load. The command
searches dir for all files whose names match any of the
pattern arguments (matching is done with the glob
command), generates an index of all the Tcl command procedures defined
in all the matching files, and stores the index information in a file
named tclIndex in dir. If no pattern is given a pattern of
*.tcl will be assumed. For example, the command

auto_mkindex foo *.tcl

will read all the .tcl files in subdirectory foo and
generate a new index file foo/tclIndex.

Auto_mkindex parses the Tcl scripts by sourcing them into a
slave interpreter and monitoring the proc and namespace commands that
are executed. Extensions can use the (undocumented)
auto_mkindex_parser package to register other commands that can
contribute to the auto_load index. You will have to read through
auto.tcl to see how this works.

Auto_mkindex_old parses the Tcl scripts in a relatively
unsophisticated way: if any line contains the word proc
as its first characters then it is assumed to be a procedure
definition and the next word of the line is taken as the
procedures name.
Procedure definitions that do not appear in this way (e.g. they
have spaces before the proc) will not be indexed. If your
script contains
dangerous
code, such as global initialization
code or procedure names with special characters like $,
*, [ or ], you are safer using auto_mkindex_old.

auto_reset

Destroys all the information cached by auto_execok and
auto_load. This information will be re-read from disk the next
time it is needed. Auto_reset also deletes any procedures
listed in the auto-load index, so that fresh copies of them will be
loaded the next time that they are used.

auto_qualify command namespace

Computes a list of fully qualified names for command. This list
mirrors the path a standard Tcl interpreter follows for command
lookups: first it looks for the command in the current namespace, and
then in the global namespace. Accordingly, if command is
relative and namespace is not ::, the list returned has
two elements: command scoped by namespace, as if it were
a command in the namespace namespace; and command as if it
were a command in the global namespace. Otherwise, if either
command is absolute (it begins with ::), or
namespace is ::, the list contains only command as
if it were a command in the global namespace.

Auto_qualify is used by the auto-loading facilities in Tcl, both
for producing auto-loading indexes such as pkgIndex.tcl, and for
performing the actual auto-loading of functions at runtime.

tcl_findLibrary basename version patch initScript enVarName varName

This is a standard search procedure for use by extensions during
their initialization. They call this procedure to look for their
script library in several standard directories.
The last component of the name of the library directory is
normally basenameversion
(e.g., tk8.0), but it might be
library
when in the build hierarchies.
The initScript file will be sourced into the interpreter
once it is found. The directory in which this file is found is
stored into the global variable varName.
If this variable is already defined (e.g., by C code during
application initialization) then no searching is done.
Otherwise the search looks in these directories:
the directory named by the environment variable enVarName;
relative to the Tcl library directory;
relative to the executable file in the standard installation
bin or bin/arch directory;
relative to the executable file in the current build tree;
relative to the executable file in a parallel build tree.

parray arrayName

Prints on standard output the names and values of all the elements
in the array arrayName.
ArrayName must be an array accessible to the caller of parray.
It may be either local or global.

tcl_endOfWord str start

Returns the index of the first end-of-word location that occurs after
a starting index start in the string str. An end-of-word
location is defined to be the first non-word character following the
first word character after the starting point. Returns -1 if there
are no more end-of-word locations after the starting point. See the
description of tcl_wordchars and tcl_nonwordchars below
for more details on how Tcl determines which characters are word
characters.

tcl_startOfNextWord str start

Returns the index of the first start-of-word location that occurs
after a starting index start in the string str. A
start-of-word location is defined to be the first word character
following a non-word character. Returns -1 if there are no more
start-of-word locations after the starting point.

tcl_startOfPreviousWord str start

Returns the index of the first start-of-word location that occurs
before a starting index start in the string str. Returns
-1 if there are no more start-of-word locations before the starting
point.

tcl_wordBreakAfter str start

Returns the index of the first word boundary after the starting index
start in the string str. Returns -1 if there are no more
boundaries after the starting point in the given string. The index
returned refers to the second character of the pair that comprises a
boundary.

tcl_wordBreakBefore str start

Returns the index of the first word boundary before the starting index
start in the string str. Returns -1 if there are no more
boundaries before the starting point in the given string. The index
returned refers to the second character of the pair that comprises a
boundary.

The following global variables are defined or used by the procedures in
the Tcl library:

auto_execs

Used by auto_execok to record information about whether
particular commands exist as executable files.

auto_index

Used by auto_load to save the index information read from
disk.

auto_noexec

If set to any value, then unknown will not attempt to auto-exec
any commands.

auto_noload

If set to any value, then unknown will not attempt to auto-load
any commands.

auto_path

If set, then it must contain a valid Tcl list giving directories to
search during auto-load operations.
This variable is initialized during startup to contain, in order:
the directories listed in the TCLLIBPATH environment variable,
the directory named by the $tcl_library variable,
the parent directory of $tcl_library,
the directories listed in the $tcl_pkgPath variable.

env(TCL_LIBRARY)

If set, then it specifies the location of the directory containing
library scripts (the value of this variable will be
assigned to the tcl_library variable and therefore returned by
the command info library). If this variable is not set then
a default value is used.

env(TCLLIBPATH)

If set, then it must contain a valid Tcl list giving directories to
search during auto-load operations. Directories must be specified in
Tcl format, using
/
as the path separator, regardless of platform.
This variable is only used when initializing the auto_path variable.

tcl_nonwordchars

This variable contains a regular expression that is used by routines
like tcl_endOfWord to identify whether a character is part of a
word or not. If the pattern matches a character, the character is
considered to be a non-word character. On Windows platforms, spaces,
tabs, and newlines are considered non-word characters. Under Unix,
everything but numbers, letters and underscores are considered
non-word characters.

tcl_wordchars

This variable contains a regular expression that is used by routines
like tcl_endOfWord to identify whether a character is part of a
word or not. If the pattern matches a character, the character is
considered to be a word character. On Windows platforms, words are
comprised of any character that is not a space, tab, or newline. Under
Unix, words are comprised of numbers, letters or underscores.